Brothers Know
by Myra109
Summary: Sirius knew. This feeling was a dark, aching pain in his stomach, dragging him down until he collapsed on the floor of the Potters' home, twitching and screaming, muttering his name. He doesn't know how, but he knew. Regulus was in trouble. AU


_Just a fairly short one shot._

 ** _Disclaimer: I do not own Harry Potter._**

* * *

He _knew_.

Sirius didn't know how or why, but from the minute he woke up, something felt terribly, dangerously wrong. He just knew something wasn't right, but he couldn't put his finger on it.

Until just after lunch, that is.

Sirius had played with his food all through the meal and somehow got away with barely eating half of his food (an impressive feat since Mrs. Potter was usually the type to watch your eating like a hawk). James and him walked into the living room, followed by Mr. and Mrs. Potter; James was bubbling with fun ideas for activities to do that day (as usual, starting with Quidditch), but Sirius's heart wasn't in it. If the Potters noticed his quiet and almost sluggish and downright weird behavior, which it was unlikely they did, they didn't say anything.

And then the feeling hit it's peak, and Sirius finally realized what was causing the feeling.

Sirius knew. This feeling was a dark, aching pain in his stomach, dragging him down until he collapsed on the floor of the Potters' home, twitching and screaming, muttering his name. He doesn't know how, but he _knew_. Regulus was in trouble.

Sirius started convulsing, almost like he was having a seizure, and he could hear James calling his name. Mrs. Potter had his head in her lap as Sirius tossed it back and forth, causing a dull ache in his neck; Mr. Potter was holding his hand, asking what was wrong.

And then it stopped. Sirius froze; the convulsions halted, and he lay perfectly still, staring at the ceiling.

The Potters waited, anxiously, for a reaction. Any reaction.

Sirius sat bolt up right, making James, who he nearly headbutted, to leap backwards.

"He's in trouble," Sirius muttered, standing, despite the family's best efforts to force him to sit back down.

"Who?" Mr. Potter demanded, but Sirius was already halfway to the fireplace.

"Regulus," Sirius stated, simply, stepping into the fireplace and tossing a handful of Floo Power at his feet. "Grimmauld Place Number Twelve!" He called.

Emerald flames consumed him, and Sirius felt himself being tugged in every direction, making his stomach flop with nerves and motion sickness. He was abruptly spat out onto an expensive rug, covered in soot and coughing up ashes.

"What are you doing here?" His biological father spat. "Come crawling back?"

"Where's Regulus?" Sirius asked.

Orion frowned. Whatever he'd been expecting Sirius to say, it hadn't been that.

The man quickly regained his composure and rolled his eyes.

"Why do you want to know?" He questioned. "You turned your back on-"

"Where is he?" Sirius roared, making his shocked father jump.

"He went for a walk, down by the lake. I don't know why; it's freezing out there," Orion muttered, turning back to his newspaper as Sirius bolted for the back door.

Sirius flew across the ground, kicking up snow left and right. He cut between houses, even through some houses (that freaked some people out), and Sirius leaped over a swing, making the kid on the swing next to it cry out in surprise.

"Have you gone mad?" He heard James call from a good distance behind him.

"Possibly!" Sirius yelled back over his shoulder.

Sirius continued sprinting until he reached the edge of the frozen lake.

There was no one in sight.

Sirius _knew._

The elder brother dashed out on the ice, throwing caution to the wind, and he stumbled, sinking knee deep into the blanket of snow covering the water.

Sirius skidded to a halt and fell to his knees in the middle of the ice.

His fingertips grazed a circle of exposed ice, the snow having been kicked to the side, and he pressed on it. It felt warm to the touch...

Sirius had seen this before. Professors had used it on the Black Lake, using it to mend any broken ice and seal any holes students could fall through, while making the ice thicker.

A spell. Or a hex, depending on how you used it.

"What is going on?" James sputtered as he appeared beside Sirius. His parents had stayed on the shore since their weight could possibly break the ice.

"Regulus is under there," Sirius said.

James frowned. "How do you know?"

"Brothers know!" Sirius stated, simply. "Now, help me look!"

James and Sirius sprouted off in separate directions, swiping and kicking ice aside. Sirius's breath hitched as he caught sight of a hint of color beneath the surface, and he started swiping ice aside, using his palm to wipe a thick layer of frost away.

Regulus was just below the frozen surface. He was still moving, kicking his legs, but his movements were dangerously sluggish and the amount of movement was dwindling, rapidly.

Sirius withdrew his wand from his pocket and yelled a breaking spell at the ice, but it didn't budge.

"Whoever hexed the ice... their magic is too strong. I can't break through it!" Sirius cried, banging his fists against the thick layer of ice.

Below the surface, Regulus stopped moving, completely, and his head slumped forward.

With a scream that people heard almost a mile away, Sirius felt his hands become burning hot, and the ice melted below his skin, hissing as it became water.

Sirius's hands wrapped around Regulus's upper arms, dragging him onto the frozen surface.

Regulus lay on the ice, unmoving. His face was deathly pale, and his lips were a sickening blue color. His eyes remained closed, and his chest didn't move.

Sirius heard Mr. and Mrs. Potter running across the ice, and Sirius cast a spell to push the water out of Regulus's lungs.

Nothing happened.

James drew his own wand and cast the spell at the same time as Sirius.

Nothing.

The two Marauders tried again, even more desperately than before.

This time, Regulus coughed, spitting water out of his mouth and breathing, deeply, seemingly surprised that he was inhaling oxygen instead of water.

"Reg!" Sirius exclaimed.

Regulus breathed, heavily, after forcing the last of the water out of his lungs, and he stared up at Sirius, too disoriented to comprehend the situation. His oxygen deprived mind barely seemed to recognize Sirius.

But then he smiled, weakly.

"Siri," he rasped.

Sirius nodded with a smile of his own, and Mr. Potter knelt beside Regulus, lifting the boy as though he weighed no more than air with one arm around his shoulders and the other under his knees.

Regulus leaned his head against Mr. Potter's shoulder, exhaustion dragging him into a deep sleep, as they carried him back to Grimmauld Place.

James opened the door, and Mr. Potter rested Regulus in front of the blazing fire while Sirius wrapped him in a blanket.

"What happened?" His mother's detached voice asked from the doorway.

"Someone trapped him under the ice at the lake," Sirius told her. "Do you know who it was, Regulus?"

Regulus's eyes remained fixed on the flames.

He slowly nodded. "It was Bella" he whispered so quietly, it could have passed for a breath.

His mother exploded. "You dare accuse your cousin? Liar!" She bellowed.

"I'm not lying, Mother. I promise," Regulus begged. "I-I thought she was playing a prank on me, but then, she left me there! Please, Mother-"

"No," she snarled, crossing the floor to stand beside Regulus. "I won't have a liar in my house. Come on," she growled, grabbing his shoulder and dragging him to his feet.

"Mother, he shouldn't be standing-" Sirius began, but his mother had already dragged him down the hall.

She reappeared a few moments later without Regulus.

"Mother, he needs to get warm, or he'll get sick-"

"Oh, he's sick, all right! Sick enough to accuse Bellatrix of trying to kill him," she sneered.

"Mother, he's not lying. Bella isn't innocent!"

"Oh, I didn't say that, but she tries to purify our community! She doesn't kill or even maim purebloods unless they're blood traitors."

"Oh, yeah? What about that time she tried to drown us in the bathtub when I was four and Reggie was two?"

"That was a misunderstanding."

"What about that time she tried to trick Regulus into exploring the boiler room when he was four?"

"She was testing Regulus's intelligence. He should've known better."

"He didn't even know what a boiler room was. What about that time she spent hours cutting me with a knife and made Regulus watch?"

"You misbehaved, and she wanted to make sure he didn't make the same mistakes."

"She is sadistic! I-"

"You know what? If you think Regulus is in danger here, why don't you take him with you? He's been defending you whenever I criticized you ever since you ran away," she snapped. "It's only a matter of time before he becomes just like you. Might as well kill the virus before it spreads any further."

Sirius was touched about Regulus defending him, and he looked to Mr. and Mrs. Potter.

Mrs. Potter laughed. "We'd be glad to take him in."

Sirius walked down the hall and climbed the steps to the second floor, where he peaked into Regulus's room.

It was empty.

Sirius sighed. He knew where she would take Regulus in such an angry mood.

Sirius walked a little farther down the hall and opened the door under the staircase that led to the third floor.

Regulus lay on the ground, still drenched and shivering. He wasn't crying, but he looked like he was close to it.

This was a common punishment for the brothers. As children, they were free spirited and always hyper and energetic, so being cooped up in such a small space was awful. As they got older, long hours or even days spent in the closet made them terribly claustrophobic, making the punishment worse.

Sirius helped his brother, relieved at escaping the closet, stand. He explained the situation to his brother, who retrieved his trunk and a backpack from under his bed. A bag that was already packed.

"Were you planning on running away?" Sirius asked.

Regulus shrugged. "I wouldn't say _planning_. But if things got too bad or too violent or they kicked me out or whatever, and I had to leave, I wanted to be prepared."

Sirius nodded and took his brother's trunk, smiling as his brother grabbed one last thing off the bed and stuffed it in his bag- his stuffed cat, which Andromeda had given to him when he was younger.

"Thanks for this," Regulus told the Potters as they arrived at the fireplace.

Mr. Potter grinned. "No problem, Regulus. Come along."

The five of them stepped through the Floo, and Sirius showed Regulus to one of the guest rooms (which would eventually be known as Regulus's room once they added some things to make it look like Regulus's).

"Sirius," Regulus said as he set his trunk down at the foot of his bed. "Thanks for saving me."

Sirius chuckled. "You never need to thank me for saving your life, Reg. I'm your older brother. Brothers protect each other."

"How did you know I was in trouble?" Regulus asked.

Sirius shrugged. "Brothers know," he told him, simply. "Welcome home, Reggie."

Regulus's face lit up at the thought of staying in a house that might actually feel like _home_.

* * *

 _I don't know why, but I have just been so interested in writing 'falling through ice and getting trapped under it' stories lately. I think it was because I watched a scene in a TV show called Riverdale where a character gets trapped under the ice on a lake, and I just loved the suspense._

 _Anyway, I hope you all liked it. Please leave a review! Thanks for reading! Bye!_


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